Bug 1405585 - Add telemetry to watch inspector delay between new-root event and full update. r=francois,jdescottes datareview=francois

MozReview-Commit-ID: 5cWcTxPvDKF

--HG--
extra : rebase_source : 9e1a2c4b6aa6eee200c4d653b951f4e5e9cd0e9a

devtools/client/inspector/inspector.js

@@ -848,6 +848,9 @@ Inspector.prototype = {
    * Reset the inspector on new root mutation.
    */
   onNewRoot: function () {
+    // Record new-root timing for telemetry
+    this._newRootStart = this.panelWin.performance.now();
+
     this._defaultNode = null;
     this.selection.setNodeFront(null);
     this._destroyMarkup();
@@ -900,6 +903,18 @@ Inspector.prototype = {
     yield onExpand;
 
     this.emit("reloaded");
+
+    // Record the time between new-root event and inspector fully loaded.
+    if (this._newRootStart) {
+      // Only log the timing when inspector is in foreground.
+      if (this.toolbox.currentToolId == "inspector") {
+        let delay = this.panelWin.performance.now() - this._newRootStart;
+        let telemetryKey = "DEVTOOLS_INSPECTOR_NEW_ROOT_TO_RELOAD_DELAY_MS";
+        let histogram = Services.telemetry.getHistogramById(telemetryKey);
+        histogram.add(delay);
+      }
+      delete this._newRootStart;
+    }
   }),
 
   _selectionCssSelector: null,

toolkit/components/telemetry/Histograms.json

@@ -8446,6 +8446,16 @@
     "keyed": true,
     "description": "Time taken (in ms) to update DevTools panel when reloading a page. This is keyed by tool ID being currently opened [inspector, webconsole, jsdebugger, styleeditor, shadereditor, canvasdebugger, performance, memory, netmonitor, storage, webaudioeditor, scratchpad, dom]."
   },
+  "DEVTOOLS_INSPECTOR_NEW_ROOT_TO_RELOAD_DELAY_MS": {
+    "record_in_processes": ["main"],
+    "alert_emails": ["dev-developer-tools@lists.mozilla.org", "hkirschner@mozilla.com"],
+    "bug_numbers": [1405585],
+    "expires_in_version": "62",
+    "kind": "exponential",
+    "high": 120000,
+    "n_buckets": 100,
+    "description": "Time taken (in ms) to update the inspector during a page reload, starting from new-root event."
+  },
   "DEVTOOLS_DEBUGGER_DISPLAY_SOURCE_LOCAL_MS": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",